The semiconductor industry is currently considering the use of thin metal or metal containing films for a variety of applications. Many organometallic complexes have been evaluated as potential precursors for the formation of these thin films.
U.S. Patent Application Publication No. US2009302434A and WO09149372A disclose methods and compositions for depositing rare earth metal-containing layers. In general the disclosed methods deposit the precursor compounds comprising rare earth metal-containing compounds using deposition methods such as chemical vapor deposition or atomic layer deposition. The disclosed precursor compounds include a cyclopentadienyl ligand having at least one aliphatic group as a substituent and an amidine ligand.
The tutorial review by Edelmann, F. T. “Lanthanide Amidinates and Guanidinates: From Laboratory Curiosities to Efficient Homogeneous Catalysts and Precursors for Rare-Earth Oxide Thin Films.” Chemical Society Reviews 38(8): 2253-2268 (2009) teaches that a hot topic in current organolanthanide chemistry is the search for alternative ligand sets which are able to satisfy the coordination requirements of the large lanthanide cations. Among the most successful approaches in this field is the use of amidinate ligands of the general type [RC(NR′)2]− (R=H, alkyl, aryl; R′=alkyl, cycloalkyl, aryl, SiMe3) which can be regarded as steric cyclopentadienyl equivalents. Closely related are the guanidinate anions of the general type [R2NC(NR′)2]− (R=alkyl, SiMe3; R′=alkyl, cycloalkyl, aryl, SiMe3). Two amidinate or guanidinate ligands can coordinate to a lanthanide ion to form a metallocene-like coordination environment which allows the isolation and characterization of stable though very reactive amide, alkyl, and hydride species. Mono- and trisubstituted lanthanide amidinate and guanidinate complexes are also readily available. Various rare earth amidinates and guanidinates have turned out to be very efficient homogeneous catalysts e.g. for ring-opening polymerization reactions. Moreover, certain alkyl-substituted lanthanide tris(amidinates) and tris(guanidinates) were found to be highly volatile and could thus be promising precursors for ALD (=Atomic Layer Deposition) and MOCVD (=Metal-Organic Chemical Vapor Deposition) processes in materials science and nanotechnology. This tutorial review covered the success story of lanthanide amidinates and guanidinates and their transition from mere laboratory curiosities to efficient homogeneous catalysts as well as ALD and MOCVD precursors.
Husekova, K., M. JurkoviC, K. Cico, D. Machajdik, E. DobroCka, R. Luptak, A. Mackova and K. Frohlich “Preparation of High Permittivity GdScO3 Films by Liquid Injection MOCVD.” ECS Transactions 25(8): 1061-1064 (2009) teach the preparation and properties of GdScO3 thin films. The films were prepared by liquid injection metal-organic chemical vapor deposition, MOCVD at 600° C. on (100) Si substrate. The as-deposited films were amorphous with a smooth surface and sharp GdScO3/Si interface. X-ray diffraction showed that the amorphous phase is well preserved upon rapid thermal annealing up to 1000° C. However, modification of the X-ray reflectivity pattern after annealing at 1000° C. indicates increasing of the film thickness, presumably due to diffusion of silicon from the substrate into the whole volume of the film. Capacitance-voltage measurement resulted in dielectric constant of 22. It is shown, that exact stoichiometry of GdScO3 is not necessary to achieve dielectric constant above 20.
Jones, A. C., H. C. Aspinall, P. R. Chalker, R. J. Potter, K. Kukli, A. Rahtu, M. Ritala and M. Leskela “Recent Developments in The MOCVD and ALD of Rare Earth Oxides and Silicates.” Materials Science and Engineering B 118(1-3): 97-104 (2005) investigate lanthanide, or rare-earth as alternatives to SiO2 as the dielectric insulating layer in sub-0.1 μm CMOS technology. Metalorganic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) are promising techniques for the deposition of these high-K dielectric oxides and in this paper some of our recent research into the MOCVD and ALD of PrOx, La2O3, Gd2O3, Nd2O3 and their related silicates are reviewed.
Japanese patent application No, JP2002338590 A2 discloses 11 tris(ethylcyclopentadienyl)lanthanides represented by general formula Ln(C5H4Et)3 (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) are prepared by reaction of anhydrous lanthanide chloride with ethylcyclopentadienyl potassium in THF or an inert organic solvent containing THF, removing a salt formed and distilling off unreacted reactants, THF, solvent, and byproducts under reduced pressure, and vacuum distillation to recover the product.
Katamreddy, R., N. A. Stafford, L. Guerin, B. Feist, C. Dussarrat, V. Pallem, C. Weiland and R. Opila “Atomic Layer Deposition of Rare-Earth Oxide Thin Films for High-K Dielectric Applications” ECS Transactions, 19(2): 525-536 (2009) propose many different organolanthanide molecules as metal sources for depositing metal and metal oxide layers for semiconductors by atomic layer deposition (ALD). These precursors needed particular physical and thermal properties to be used in the semiconductor manufacturing process. For example, the precursors needed to have high volatility, reactivity, and thermal stability. ALD deposition methods were very promising; however, new high-K metal oxide films would require new precursors to meet the very stringent requirements of the semiconductor process. Tris(cyclopentadienyl) rare earth compounds are interesting for use as precursors because of their high vapor pressures, often low melting points and availability in the liquid state, high reactivity towards water, and high growth rates for deposition. In this study, the various important thermal properties of Cp-based lanthanide precursors along with their ALD properties for metal oxide deposition were studied.
U.S. Patent Application Publication No. US20080032062A1 discloses organometallic compounds represented by the formula M(NR1R2)x wherein M is a metal or metalloid, R1 is the same or different and is a hydrocarbon group or a heteroatom-containing group, R2 is the same or different and is a hydrocarbon group or a heteroatom-containing group; R1 and R2 can be combined to form a substituted or unsubstituted, saturated or unsaturated cyclic group; R1 or R2 of one (NR1R2) group can be combined with R1 or R2 of another (NR1R2) group to form a substituted or unsubstituted, saturated or unsaturated cyclic group; x is equal to the oxidation state of M; and wherein said organometallic compound has (i) a steric bulk sufficient to maintain a monomeric structure and a coordination number equal to the oxidation state of M with respect to anionic ligands, and (ii) a molecular weight sufficient to possess a volatility suitable for vapor deposition; a process for producing the organometallic compounds, and a method for producing a film or coating from organometallic precursor compounds.
Nief, F. “Heterocyclopentadienyl Complexes of Group-3 Metals.” European Journal of Inorganic Chemistry(4): 891-904 (2001) teaches that heterocyclopentadienyl complexes of group-3 metals (scandium, yttrium, lanthanum and the lanthanides, and uranium) are compounds in which one or more —CH units of a cyclopentadienyl-like ligand have been replaced by a heteroelement (nitrogen, phosphorus, arsenic, or antimony). These ligands can have very diverse substitution patterns, notably with bridged and cavitand-like structures. In addition to the classical η5-coordination behaviour, the heterocyclopentadienyl ligand can adopt a very large array of coordination patterns. Some complexes have a very promising chemistry since they have been found to activate small molecules such as nitrogen and ethylene.
Päiväsaari, J. and I. Charles L. Dezelah, Dwayne Back, Hani M. El-Kaderi, Mary Jane Heeg, Matti Putkonen, Lauri Niinistö and Charles H. Winter “Synthesis, structure and properties of volatile lanthanide complexes containing amidinate ligands: application for Er2O3 thin film growth by atomic layer deposition.” J. Mater. Chem. 15: 4224-4233 (2005) teach the treatment of anhydrous rare earth chlorides with three equivalents of lithium 1,3-di-tert-butylacetamidinate (prepared in situ from the di-tert-butylcarbodiimide and methyllithium) in tetrahydrofuran at ambient temperature afforded Ln(tBuNC(CH3)NtBu)3 (Ln=Y, La, Ce, Nd, Eu, Er, Lu) in 57-72% isolated yields. X-Ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions. These new complexes are thermally stable at >300° C., and sublime without decomposition between 180-220° C./0.05 Torr. The atomic layer deposition of Er2O3 films was demonstrated using Er(tBuNC(CH3)NtBu)3 and ozone with substrate temperatures between 225-300° C. The growth rate increased linearly with substrate temperature from 0.37 Å per cycle at 225° C. to 0.55 Å per cycle at 300° C. Substrate temperatures of >300° C. resulted in significant thickness gradients across the substrates, suggesting thermal decomposition of the precursor. The film growth rate increased slightly with an erbium precursor pulse length between 1.0 and 3.0 s, with growth rates of 0.39 and 0.51 Å per cycle, respectively. In a series of films deposited at 250° C., the growth rates varied linearly with the number of deposition cycles. Time of flight elastic recoil analyses demonstrated slightly oxygen-rich Er2O3 films, with carbon, hydrogen and fluorine levels of 1.0-1.9, 1.7-1.9 and 0.3-1.3 atom %, respectively, at substrate temperatures of 250 and 300° C. Infrared spectroscopy showed the presence of carbonate, suggesting that the carbon and slight excess of oxygen in the films are due to this species. The as-deposited films were amorphous below 300° C., but showed reflections due to cubic Er2O3 at 300° C. Atomic force microscopy showed a root mean square surface roughness of 0.3 and 2.8 nm for films deposited at 250 and 300° C., respectively.
Peng, H., Z. Zhang, R. Qi, Y. Yao, Y. Zhang, Q. Shen and Y. Cheng “Synthesis, Reactivity, and Characterization of Sodium and Rare-Earth Metal Complexes Bearing a Dianionic N-Aryloxo-Functionalized β-ketoiminate Ligand.” Inorganic Chemistry 47(21): 9828-9835 (2008) teach the synthesis and reactivity of a series of sodium and rare-earth metal complexes stabilized by a dianionic N-aryloxo-functionalized β-ketoiminate ligand. The reaction of acetylacetone with 1 equivalent of 2-amino-4-methylphenol in absolute ethanol gave the compound 4-(2-hydroxy-5-methylphenyl)imino-2-pentanone (LH2, 1) in high yield. Compound 1 reacted with excess NaH to afford the novel sodium cluster [LNa2(THF)2]4 (2) in good isolated yield. Structure determination revealed that complex 2 has the 22-vertex cage structure. Reactions of complex 2 with anhydrous LnCl3 in a 1:4 molar ratio, after workup, gave the desired lanthanide chlorides [LLnCl(DME)]2[Ln=Y (3), Yb (4), Tb (5)] as dimers. A further study revealed that complexes 3-5 are inert for chlorine substitution reactions. (ArO)3Ln(THF) (ArO=2,6-But2-4-MeC6H2O) reacted with compound 1 in a 1:1 molar ratio in tetrahydrofuran (THF), after workup, to give the desired rare-earth metal aryloxides as dimers [LLn(OAr)(THF)]2[Ln=Nd (6), Sm (7), Yb (8), Y (9)] in high isolated yields. All of these complexes are well characterized, and the definitive molecular structures of complexes 2 and 4-6 were determined. It was found that complexes 6-9 can be used as efficient initiators for L-lactide polymerization, and the ionic radii of the central metals have a significant effect on the catalytic activity.
U.S. Patent Application Publication No. US2010078601 teaches methods and compositions for depositing rare earth metal-containing layers. In general the disclosed methods deposit the precursor compounds comprising rare earth-containing compounds using vapor deposition methods such as chemical vapor deposition or atomic layer deposition. In certain embodiments the disclosed precursor compounds include a cyclopentadienyl ligand having at least one aliphatic group as a substituent.
A need still exists in the industry for developing new volatile, reactive, and thermally stable compounds as potential precursors to deposit metal containing films via chemical vapor deposition (CVD) and atomic layer deposition(ALD).
This invention is directed to a novel family of group 2 to 15 metal complexes which can be potentially used as precursors to deposit metal or metal oxide films in semi-conductor industries.